Remove duplicate save attribute.

There is already a blanket save statement for the entire module, so these save attributes induce a warning on newer compilers.

For example, with gfortran,
```
axisem/SOLVER/nc_routines.F90:107.36:
    integer, save       :: ndim_disp !< 2 for monopole, 3 for rest
                                    1
Warning: Legacy Extension: Duplicate SAVE attribute specified at (1)
```